Japanese government is bringing on board additional three satellites to the country’s domestic navigation satellite systems in order to ensure that it would work with or without the U.S.’s GPS systems.The Quasi-Zenith Satellite System (QZSS) is a regional navigation satellite system commissioned by the Japanese Government as a National Space Development Program.
QZSS was authorized by the Japanese government in 2002. At the beginning the system was developed by the Advanced Space Business Corporation (ASBC) team, including Mitsubishi Electric Corp., Hitachi Ltd., and GNSS Technologies Inc. When in 2007 ASBC collapsed, the work was taken over by JAXA together with Satellite Positioning Research and Application Center (SPAC), established in February 2007 and approved by the Ministers associated with QZSS research and development.
Colonel Shinichiro Tsui, a counsellor in Japan’s Cabinet Office, said that the next three QZSS satellites are all scheduled to launch this year, followed by service activation in 2018. Those satellites, provided by manufacturer Mitsubishi Electric, would augment GPS signals, Tsui said, honing their positioning accuracy from sub-meter to centimeters. But to have a navigation system capable of functioning independently from the U.S., the constellation would need at least seven satellites.
“[To] have accurate positioning data, we need to have four satellites, which means still we need a GPS satellite from space,” he explained. “But if we have seven QZSS … [even] if we don’t have any GPS signals, we still have Japan’s own navigation capability.”
QZSS uses three satellites, each 120° apart, in highly inclined, slightly elliptical, geosynchronous orbits. Because of this inclination, they are not geostationary; they do not remain in the same place in the sky. Instead, their ground traces are asymmetrical figure-8 patterns (analemmas), designed to ensure that one is almost directly overhead (elevation 60° or more) over Japan at all times.
The nominal orbital elements are:
|Epoch||2009-12-26 12:00 UTC|
|Semimajor axis (a)||42,164 km|
|Eccentricity (e)||0.075 ± 0.015|
|Inclination (i)||43° ± 4°|
|Right ascension of the ascending node (Ω)||195° (initial)|
|Argument of perigee (ω)||270° ± 2°|
|Mean anomaly (M0)||305° (initial)|
|Central longitude of ground trace||135° E ± 5°|
QZSS is targeted at mobile applications, to provide communications-based services (video, audio, and data) and positioning information. With regards to its positioning service, QZSS can only provide limited accuracy on its own and is not currently required in its specifications to work in a stand-alone mode. As such, it is viewed as a GNSS Augmentation service.
Its positioning service could also collaborate with the geostationary satellites in Japan’s Multi-Functional Transport Satellite (MTSAT), currently under development, which itself is a Satellite Based Augmentation System similar to the U.S. Federal Aviation Administration’s Wide Area Augmentation System (WAAS).